1. Field of the Invention
The present invention relates to a retractable knife, and more particularly to an assisted-opening knife using a spring to rapidly expand the blade and having a latch mechanism preventing the blade from being unlocked during cutting and stabbing.
2. Description of the Related Art
Retractable knives are very common tools for cutting things. As the retractable knives can be retracted and fully received in a holder when not in use, users can be prevented from being inadvertently wounded by the exposed blade. The popularity of the retractable knives is basically established on the safety protection.
With reference to FIG. 8, a conventional retractable knife has a holder 90, a blade 91 and a slider 92. The holder 90 takes a form of a flat and elongated box and has a top opening 93 (not shown), a front opening and a corrugated portion 94. The top opening 93 is formed through a top of the holder 90. The front opening takes a form of a slit, is formed through a front edge of the holder 90 and communicates with the top opening 93. The corrugated portion 94 is formed on a longitudinal inner side of the top opening 93 and has a plurality of peaks and valleys. The blade 91 is elongated and is slidably mounted in the holder 90 through the front opening. The slider 92 is fastened on a rear end of the blade 91 and has a stopper 95 mounted on one side of the slider 92 that is in parallel with the longitudinal inner side of the top opening. When the slider 92 is pushed and slidably moved to one of the valleys of the corrugated portion 94, the stopper 95 engages the valley, the blade 91 is temporarily locked, and a proper length of the blade 91 is extended or retracted.
Due to the engagement between the stopper 95 and the corrugated portion 94, the blade 91 can be held at an intended position in a stepwise manner which is not an efficient way to promptly move the blade 91. Besides, when the stopper 95 is facilitated to slide between the peaks and valleys of the corrugated portion 94, the stopper 95 does not tightly engage the corrugated portion 94. As a consequence, the stopper 95 easily disengages from a valley when the cutter knife is used to stab or cut things forcefully, and the blade 91 fails to be securely locked at an intended position for continuous cutting. Fingers of a user are easily pinched in the top opening 93 by the slider 92. To overcome the aforementioned drawbacks, the conventional retractable knife needs to be further developed.